Axial piston machine

ABSTRACT

The invention relates to an axial piston machine, in particular, an air-conditioning compressor for motor vehicles, with at least one piston, an essentially cylindrical piston shaft and an enclosure, which encloses a tilt ring or a tilt disc and a piston slipper sliding on said tilt ring or said tilt disc, whereby the enclosure has spherical recesses for housing the piston slipper.

The present invention relates to an axial piston machine, in particular,an air-conditioner compressor for motor vehicles, including at least onepiston having a substantially cylindrical piston body and a brace thatembraces a tilting ring or a tilting plate and piston shoes sliding onsaid tilting ring or said tilting plate; the brace having sphericalcap-shaped depressions for receiving the piston shoes, said depressionsbeing located on the side of the piston body and on the opposite side.

Axial piston engines of this kind are generally known. These axialpiston engines have the disadvantage of requiring special machines orspecial devices for machining the spherical shape of the sphericalcap-shaped depressions in the brace of the piston. The machining iscarried out under interrupted cutting conditions, that is, the cuttingtool moves out of and back into the workpiece during machining.Moreover, with the known machining methods, it is not possible toprovide the edges of the spherical shape with lubricating wedge chamfersin a cost-effective manner. In the known machining processes, thespherical shape in the brace is machined with the cylinder axis of thepiston in a fixed chucking position. In this connection, it is possible,inter alia, to produce the spherical shape by rotating the piston aboutan axis extending perpendicular to its cylinder axis and through thecenter of the sphere during the machining of the spherical form.However, these methods are cumbersome and error-prone and, as mentionedearlier, require special machines or special devices.

Also, the piston braces of known pistons project radially outwardrelatively far from the piston axis so as to provide sufficient spacefor the movement of the tilting plate or tilting ring and the pistonshoes, while being sufficiently stiff to prevent the piston shoes fromfalling out.

Moreover, in tilting-ring or tilting-plate type compressors, thelubrication of the radially outward sliding surface of the brace betweenthe piston and the housing is of great importance, especially if, whenusing CO₂ as the refrigerant, the machine dimensions are smaller than inconventional refrigerant compressors because of the high pressures. As aconsequence of the tight spaces in a CO₂ compressor, the spaces betweenthe pistons where lubricant can be distributed, for example, in thedrive chamber, become narrower and narrower. The larger the peripheralhousing region covered by the piston brace is compared to the exposedperipheral region of the housing, the more difficult is it to supplylubricant to this region. If in tilting plate machines or tilting ringmachines of this type, such as for CO₂ applications, the degree ofcoverage by the piston brace becomes relatively high so that there areonly small gaps between the individual piston brace regions forintroducing lubricant between the peripheral regions, insufficientlubricant supply and friction damage may occur in this area.

It is, therefore, the object of the present invention to devise an axialpiston machine which will overcome these disadvantages.

This objective is achieved firstly by an axial piston machine, inparticular, an air-conditioner compressor for motor vehicles, includingat least one piston having a substantially cylindrical piston body and abrace that embraces a tilting ring or a tilting plate and piston shoessliding on said tilting ring or on said tilting plate; the brace havingspherical cap-shaped depressions for receiving the piston shoes, saiddepressions being located on the side of the piston body and on theopposite side; and the brace having an opening in its side opposite thepiston body. A preferred axial piston machine is one in which the axisof the opening coincides with the axis of the piston body.

Also preferred is an axial piston machine, in which the opening issubstantially cylindrical. Another preferred axial piston machine is onein which a tool for machining the spherical cap-shaped depressions inthe brace can be introduced through the opening. An axial piston machineaccording to the present invention is characterized in that themachining motion for producing the spherical shape of the sphericalcap-shaped depressions can be produced by rotating the piston about theaxis of the piston body, that is, about the cylinder axis. This allowsthe spherical cap shapes to be produced by turning on standard lathes.

Another axial piston machine according to the present invention may havea centering hole or a centering center or a weight-reduction holedisposed on the piston body side of the brace opposite the brace sideprovided with the opening. Preferred is a piston in which a coating ofthe piston can be machined on lathes and grinding machines in a verystable chucking position by using the centering center.

A further preferred axial piston machine is one in which the sphericalcap-shaped depressions can be produced using reversible inserts having aready-made spherical contour.

Also preferred is an axial piston machine in which the piston can bemanufactured as a single, solid piece from an aluminum material.

An axial piston machine according to the present invention ischaracterized in that a first spherical recess is disposed within thebridge of the brace, that is, in the inner radial region of the pistonbrace. A preferred axial piston machine is one in which the firstspherical recess can be produced by rotating the piston about itscylinder axis with the tool rotating during the machining of thespherical shape in the brace.

In another axial piston machine according to the present invention, thefirst spherical recess can be produced by rotating the piston about anaxis extending perpendicular to its cylinder axis without the toolrotating during the machining of the spherical shape in the brace.

Moreover, the spherical running surfaces of the piston shoes in thebrace can seamlessly merge into the first spherical recess in the bridgeof the brace, and the spherical running surfaces and the first sphericalrecess can preferably have equal sphere radii. Also preferred is a firstspherical recess which can be processed by and during the machining ofthe piston shoe bearing surfaces, or fully produced by this machiningprocess. Preferably, the bridge of the brace is adapted, on its innerside, to the contour of the tilting ring or tilting plate by a secondspherical recess of larger radius outside the first spherical recess. Inaccordance with the present invention, the second spherical recessallows the bridge of the brace to be shifted as close as possible to thetilting ring or tilting plate. This reduces the bending load on thebrace by shorter lever arms. The first spherical recess only slightlyreduces the stiffness of the brace, because the first spherical recessis located very close to the bending line. This is made possible becausethe second spherical recess shifts the bending line of the brace soclose to the tilting plate or tilting ring that the stiffness againstbending during the suction movement is only slightly reduced compared toa brace without a first spherical recess. Because of this, less materialand installation space are needed, which reduces costs.

It is a feature of an axial piston machine according to the presentinvention that the cylindrical piston body and the brace are twoseparate parts from which the piston can be assembled. The advantage ofthis is that the materials and manufacturing methods for thesedifferently shaped parts can be adapted to the different loads.

Also preferred is an axial piston machine whose brace can be made from astrip of sheet metal and, after suitably shaping the metal strip, isconnectable to the cylindrical piston body, which can be made as adeep-drawn part of sheet metal. Another preferred axial piston machineis one in which the opening in the brace can be made by punching. Also,the seating of the piston shoes can be produced or largely preformedduring the forming process of the brace. Also preferred is an axialpiston machine in which the cylindrical piston body and the brace can bemade from a steel material. A further preferred axial piston machine isone in which the brace and the cylindrical piston body can be joinedtogether by laser welding or resistance welding. Moreover, the hollowspace between the brace and the piston body can be airtight, or nearlyairtight.

Another embodiment of the axial piston machine according to the presentinvention is characterized in that, after the brace and the piston bodyare assembled together, the piston is first provided with an adhesivebase coat, for example by phosphating, in a layer thickness of about 2-3μm, and then provided with a surface coating of PTFE in a layerthickness of about 10 μm.

The objective is also achieved by an axial piston machine in which theouter side, as a sliding surface, of the brace has at least one openingto the inner radial region of the brace which faces the tilting plate ortilting ring. Preferably, the at least one opening serves to supplylubricant to the sliding surface, because the sliding surface is locatedin the peripheral region covered by the piston brace and, therefore, canonly with difficulty be supplied with the lubricant contained in therefrigerant in the drive mechanism housing.

In a further embodiment of the axial piston machine according to thepresent invention, the peripheral region of the piston brace which isdesigned as a sliding surface has several and/or differently shapedopenings or opening regions.

A preferred axial piston machine is one in which the peripheral regionof the piston brace which is designed as a sliding surface has formedtherein pocket-shaped regions opposite the drive mechanism housing wallwhich serves as a running surface, said pocket-shaped regions beingsupplied via at least one lubrication opening.

The above-mentioned embodiments allow the peripheral region covered bythe piston brace to be supplied with lubricant that is spun off of therotating tilting plate or tilting ring by centrifugal forces and thusenters the space between the piston and the housing wall through theopenings.

The present invention will now be described with reference to thefigures, in which:

FIG. 1 is a cross-sectional view of a two-part piston;

FIG. 2 shows the same piston in a side view;

FIG. 3 shows the same piston in a perspective view;

FIG. 4 illustrates the machining of the rear spherical cap;

FIG. 5 illustrates the machining of the front spherical cap;

FIG. 6 is a top view of a piston;

FIG. 7 shows a piston with a first spherical recess;

FIG. 8 illustrates the pressures determining the axial forces on thepiston;

FIG. 9 shows four representations of the first and second sphericalrecesses;

FIG. 10 illustrates the production of the first spherical recess;

FIG. 11 shows a piston in a portion of a tilting ring machine;

FIG. 12 is a cross-sectional view through a piston brace;

FIG. 13 is a top view of a piston;

FIG. 14 shows the piston arrangement in the drive mechanism chamber;

FIG. 15 shows a rotating tilting plate with a piston according to thepresent invention;

FIG. 16 shows a piston having a lubricant pocket.

FIG. 1 is a cross-sectional view of a two-part piston 1, which iscomposed of a cylindrical piston body 3 and a U-shaped piston brace 5.The two parts are joined together in region 7 by laser welding. However,other joining techniques, such as resistance welding, brazing, adhesivebonding, press-fitting, crimping, or form-locking connections, such ascirclips, threads, etc., are possible as well. Cylindrical piston body 3can preferably be made from thin sheet steel using a deep drawingprocess. The use of steel sheet has the advantage that the piston bodycan have a thin-walled design in spite of high pressure loads, and thatit can advantageously be produced in large quantities by deep drawing.However, the blanks of the parts can also be produced by cold extrusion,hot extrusion, or forging. In some cases, it can be advantageous tomanufacture such a piston from aluminum materials. Piston brace 5 can bemade from a strip of sheet steel, which is then suitably shaped from aflat metal strip into the U-shaped piston brace in a stamping tool. Theuse of a two-piece design has the advantage that the two component partsof different basic shapes can be manufactured separately according totheir shapes instead of having to be formed from a single piece in amuch more complicated way. Thus, piston brace 5 can also beadvantageously made from a steel material, which provides significantlygreater resistance to the forces occurring during operation. Pistonbrace 5 has a cylindrical opening 9 at its side opposite the piston body3; center axis 11 of said cylindrical opening coinciding with centeraxis 13 of cylindrical piston body 3. On the inner side of the pistonbrace 5, opening 9 leads into a spherical cap-shaped region 15, whichserves to receive a spherical cap-shaped piston shoe (not shown here).Likewise, at the side of brace 5 next to cylindrical piston shaft 3, aspherical cap-shaped region 17 which is capable of receiving a secondpiston shoe is provided within the brace; the two piston shoes slidingon a tilting plate or tilting ring located therebetween. The portion ofbrace 5 next to piston body 3 is provided with a smaller opening 19which provides a connection to the interior of piston body 3. Pistonbody 3 is provided at its front end with two grooves 21 which serve toreceive piston sealing rings.

In FIG. 2, piston 1 of FIG. 1 is shown in a side view in which it can beseen that piston brace 5 is provided on its upper side with a beveledstep 23 leading to a raised region 25 with which piston 1 bears againsta corresponding sliding surface of the housing inside the housing.Moreover, piston body 3 has two bevels 29 and 27 leading to a region 31which has a larger diameter and acts as a guiding cylinder sectionwithin a cylinder liner. Within piston brace 5, axis 13 of cylindricalpiston body 3 crosses an axis 33, the crossing point defining the centerof a spherical shape of the spherical cap-shaped piston shoes and ofbearing regions 15 and 17, respectively.

In FIG. 3, piston 1 of FIG. 1 and FIG. 2 is depicted in a perspectiveview showing regions 35 in which a suitable coating can be applied tothe steel components by means of an adhesive base coat, especially byphosphating the entire piston in a layer thickness of about 2-3 μm, andby subsequently providing marked regions 35 with an anti-frictioncoating of PTFE in a layer thickness of about 10 μm. However, othercoatings, such as WC/C coatings, or heat treatments, such as casehardening, are conceivable as well. The two-piece piston design isespecially preferred because the different component shapes can beproduced using manufacturing processes that are optimally adapted to theshapes. As has been mentioned earlier, deep-drawing of thin sheet steelis a suitable method for cylindrical piston body 3, while initialpunching of sheet steel and subsequent bending to shape is convenientfor piston brace 5. During the punching process, it is also possible toproduce openings 9 and 19 and to preform spherical cap regions 15 and 17in advance. In some cases, however, it may also be appropriate to selectaluminum materials.

FIG. 4 is a cross-sectional view of a piston 40. In this representation,piston 40 is shown solid in cross-section and may be manufactured, forexample, from an aluminum material. Piston 40 likewise has a cylindricalpiston body 42 and a brace 44; the end of brace 44 opposite the pistonbody 42 being provided with an opening 46 which corresponds to opening 9of FIG. 1. Opening 46 allows a cutting tool 48 to be inserted into theinterior of piston brace 44. Thus, by rotation 52 about piston-cylinderaxis 50, which corresponds to cylinder axis 13 in FIG. 1, rear sphericalcap 54 can be produced by the machining motion on standard lathes, whichis not possible in the case of known forms of braces without such anopening 46. Moreover, in this machining process, a centering center 56or a weight-reduction hole (not shown) can be made in piston body 42,and a second centering center 58 can be produced on the front face ofpiston body 42, these openings allowing dimensionally stable chuckingduring further processing steps on lathes and grinding machines, forexample, for turning and grinding a coating.

FIG. 5, finally, shows the machining of the front spherical cap shape 62in brace 44. A cutting tool 60 for machining the front spherical capshape 62 is also inserted through opening 46 in brace 44, and thespherical cap shape is then produced by suitably moving tool 60 axiallyand vertically during simultaneous rotation 52 of piston 40 about axis50. This means that the piston brace has been altered by opening 46 inpiston brace 44 in such a manner that the cutting motion for machiningthe spherical shape can be produced by rotating piston 40 about axis 50of piston body 42, that is, about the cylinder axis. Therefore, neitherspecial machines nor special devices are needed; the machining is notcarried out under interrupted cutting conditions, that is, the cuttingtool does not move out of and back into the workpiece during machiningand, in addition, it is possible to provide the edges of the sphericalshape with lubricating wedge chamfers.

This results in both considerable cost savings and better quality ofmanufacture and in operational advantages for a machine having suchpistons. Of course, the present invention is not limited in its use toair-conditioner compressors, but may also be used in other axial pistonmachines, such as axial piston pumps, that use diverse tilting-ring ortilting-plate mechanisms including piston shoes. Moreover, the presentinvention allows the coating of the piston to be processed on lathes andgrinding machines in a very stable chucking position. Therefore, thistype of chucking is considerably stiffer and more accurate compared tochucking in a centering center on the left side of the brace. Asprocessing variants to the representations in FIGS. 4 and 5, it is alsopossible to use reversible inserts having a ready-made sphericalcontour. With these reversible inserts in a tool holder, it is alsopossible to machine both sides simultaneously.

FIG. 6 is a top view of a piston 1 according to the present invention.Here, the reference numerals used correspond to those in FIGS. 1 and 2again. In the top view of FIG. 6, it can be seen, in particular, thatbevel 23, which is shown in a side view in FIG. 2, leads to a raisedregion 25 on piston brace 5, said raised region serving as a suitablecontact and sliding surface with respect to the compressor housing wall.This sliding surface 25 exists both on the right and on the left side,that is, here, both at the top and bottom of FIG. 6, and serves both asa sliding surface and to prevent the piston from rotating or tiltingsideways.

FIG. 7 is a perspective view of a piston 1 having a brace 5 and a firstspherical recess 80 in the of brace 5. The components describedhereinbefore are provided with the same reference numerals as, forexample, in FIG. 1, and will not be described again in order to avoidrepetitions. Additionally shown here is first spherical recess 80, whichcan be produced simultaneously with the bearing surfaces 62 and, notvisible here, 54 for the piston shoes during machining by rotation aboutcylinder axis 50.

FIG. 8 shows the pressures and forces acting on piston 1 and pistonbrace 44, 5 during the suction stroke. During the suction stroke of thepiston, tilting ring 82 or the tilting plate pulls piston 1 out of thecylinder block by means of the piston shoes (not shown here). In thisprocess, the movement of tilting ring 82 results in forces PA actingwithin piston brace 44, 5, said forces PA being transferred to brace 44or 5 by tilting ring 82 and the piston shoe and tending to bend thebrace 44, 5 open. In addition, inside the drive chamber, drive chamberpressure PC acts on the piston cylinder surface in region 62 of pistonbrace 44, 5, said drive chamber pressure acting against suction pressurePS on the front face of cylindrical piston body 42 or 3, respectively.Thus, during operation, brace 44 or 5 of piston 1 is primarily loaded bybending during the suction movement. In order to achieve maximumpossible stiffness during this bending, the back of the brace is shiftedradially inward as close as possible to tilting ring 82 or to thetilting plate, respectively; so that, in comparison with a brace thatprojects radially further outward, recess 80 is located so close to thebending line of the brace that the stiffness against bending during thesuction movement is only slightly reduced compared to a brace that doesnot have a spherical recess 80 and which is located radially furtheroutward and therefore has longer lever arms for bending. To this end,the back of brace 44 or 5, respectively, is adapted, on its inner side,to the cylindrical contour of the tilting ring or tilting plate andtheir moving positions by a second spherical recess 81, which can beseen in FIG. 9. This results in a space-saving geometry, thus reducingthe cost of the compressor.

In FIG. 9, spherical recesses 80 and 81 in the piston brace are shown infour views. FIG. 9 a is a view of the inner side of the brace 44 or 5,respectively, showing the first spherical cap-shaped depression, thatis, spherical recess 80, in the bridge of brace 44, 5 and a secondspherical contour 81, which can occupy the entire inner side of thebrace. FIG. 9 b shows section B-B of FIG. 9 a. Front bearing surface 62for the front piston shoe can be seen within the cut brace 44 or 5. Incut region 88 of the piston ring, both the raised sliding regions 25 ofFIG. 6, which serve as a contact surface with housing contour 86, andfirst spherical recess 80 can be seen. It can also be clearly seen thatsecond spherical recess 81 provides sufficient clearance from tiltingring contour 84 and the envelope generated by its pivotal movement, andthat section B-B follows the contour of tilting ring 84 and housing 86.

FIG. 9 c shows that bearing surface 62 and/or opposite bearing surface54 can seamlessly merge into first spherical recess 80 and form aspherical shape. Similarly to FIG. 9 b, the section shows secondspherical recess 81, which is of considerably larger diameter than firstspherical recess 80, and thus is adapted to the radius of the envelopeof the tilting plate or of tilting ring 84 of FIG. 9 b.

In FIG. 9 d, spherical recess 81 of the inner surface of the brace canbe seen particularly well from the side because of the perspective view.It also becomes clear that by producing bearing surface 62 for thepiston shoe, the first spherical recess is simultaneously produced aswell.

FIG. 10 illustrates the production of first spherical recess 80 togetherwith the production of piston shoe bearing surfaces 62 and 54. While atool is rotated about an axis of rotation 90 within brace 44, the pistonis rotated about its cylinder axis 50 to produce the spherical shape inthe brace; the cutting edge of tool 92 producing the contours of bearingsurfaces 62 and 54 for the piston shoes as well as spherical recess 80.Thus, by, as it were, shifting the brace 44, 5 closer to the outercontour of the tilting plate or tilting ring, spherical recess 80 isformed in the portion of brace 44 parallel to the cylinder axis duringthe machining of the spherical shape in brace 44 when using a rotationof piston 1 about its cylinder axis 50. This allows a cost-effectivemanufacturing process to be combined with a cost- and space-savinggeometry of brace 44.

Spherical recess 80 is also formed when rotating the piston about anaxis extending perpendicular between tool rotation axis 90 and cylinderaxis 50 and running through their intersection point (center of thesphere), while a non-rotating tool cuts the spherical or nearlyspherical contour.

FIG. 11 shows a piston 101 having a cylindrical part 102 which iscapable of reciprocating in the opening of a cylinder block 103 andwhose cylindrical outer surface therefore forms the first slidingsurface with respect to cylinder block bore 113. Piston 101 merges intoa second part 104, which serves as brace for tilting plate 106 andpiston shoes 105. When tilting plate 106 rotates, piston 101 is causedto reciprocate by means of piston shoes 105, during which tilting plate106 slides between the flat sides of piston shoes 105, while the pistonshoes 105 themselves perform a kind of a wobbling motion within thepiston brace. Piston brace 104, in turn, slides in drive mechanismhousing 107, which is only partially shown, along inner wall 108, thusforming a second sliding surface 109.

FIG. 12 is a cross-sectional view through the piston brace, such as isdescribed in the present invention and shown in a top view in FIG. 13.In FIG. 13, second sliding surface 109 is pierced by an opening 111 viawhich lubricant from the interior, especially that thrown off ofrotating tilting plate 106 (FIG. 11) by centrifugal forces, is conveyedthrough the piston brace to the upper side, that is, to sliding surface109. A sliding surface 115 for the front piston shoe can be seen onpiston brace front surface 114 below the cut piston brace surface 112; apiston shoe 105 of FIG. 11 performing a wobbling motion in said slidingsurface. Opening 111 can be frustoconical in shape so as to catch thelubricant over a wider area.

FIG. 13 is a top view of a piston according to the present invention.Cylindrical piston part 101, the diameter of which is smaller than thatof the curvature of brace surface 109, is adjoined by the secondportion, piston brace 104. Located in brace part 104 is the opening 111provided for lubricant supply, which here is, for example, oval incross-section, and is surrounded by a pocket-shaped recess 116 forreceiving the lubricant. This pocket-shaped opening 116 is shown incross-section in FIG. 16. Also indicated in FIG. 13 is an adjacentpiston brace 104′, which shows that, in a machine according to thepresent invention, there is only a very small gap 117 left between thepiston braces, which may not be sufficient for lubricant supply to bracesliding surfaces 109.

FIG. 14 shows, by way of example, six piston braces in cross-section inone machine. It can be seen that there are only very narrow gaps 117between the six piston braces 104 with their sliding surfaces 109. Thismeans that lubricant that is spun off of a rotating slant or tiltingplate within the drive chamber may possibly not be able to make its wayfrom gaps 117 to the center of sliding surfaces 109.

Therefore, in accordance with the present invention, and as shown inFIG. 15, lubricant supply is provided through opening 111 in thatlubricant 118 is passed, under the action of the centrifugal forces,from the rotating slant or tilting plate or tilting ring 106 through theopening to surface 109, where it can lubricate second sliding surface109 between the drive chamber housing wall and the radial outer surfaceof piston brace 104.

FIG. 16 also shows a cross-section of a piston brace 104 according tothe present invention; the surface 109 of said piston brace beingprovided with a lubricant pocket 116 in addition to lubricant opening111; it being possible for the lubricant pocket to be made in differentshapes, as required. The purpose of this lubricant pocket is to collectthe lubricant that has passed through opening 111 above the pistonbrace, and to supply it to sliding surface 109 in sufficient quantities.

1-29. (canceled)
 30. An axial piston machine comprising: at least onepiston having a substantially cylindrical piston body, and a braceconfigured to receive at least one of a tilting ring and a tilting plateand piston shoes slidably disposed on the at least one of the tiltingring and the tilting plate, wherein the brace includes sphericalcap-shaped depressions for receiving the piston shoes, the depressionsbeing located on a first side of the brace adjacent the piston body andon a second side of the piston brace opposite the first side, whereinthe substantially cylindrical piston body and the brace are separateparts assembled together to form the piston.
 31. An axial piston machineas recited in claim 30, wherein the axial piston machine includes anair-conditioner compressor for a motor vehicle.
 32. The axial pistonmachine as recited in claim 30, wherein the brace includes a strip ofsheet metal, and the piston body includes a deep-drawn part of sheetmetal, the brace being connectable to the cylindrical piston body. 33.The axial piston machine as recited in claim 32, wherein the braceincludes a punched opening.
 34. The axial piston machine as recited inclaim 32, wherein the spherical cap-shaped depressions are producedduring a forming process of the brace.
 35. The axial piston machine asrecited in claim 30, wherein the brace and the piston body are formedfrom a steel material.
 36. The axial piston machine as recited in claim30, wherein the brace and the piston body are joined together by atleast one of laser welding and resistance welding.
 37. The axial pistonmachine as recited in claim 30, wherein the piston includes asubstantially air tight hollow space between the brace and the pistonbody.
 38. The axial piston machine as recited in claim 30, wherein theassembled piston includes a coating, wherein the coating includes aphosphate coat applied as an adhesive base in a layer thickness of about2-3 μm, and a PTFE coat applied as a second layer in a layer thicknessof about 10 μm.
 39. The axial piston machine as recited in claim 30,wherein the piston brace includes a bridge connecting the first andsecond sides of the bridge and a first spherical recess disposed withinthe bridge.
 40. The axial piston machine as recited in claim 39, whereinthe piston shoes includes spherical running surfaces that merge into thefirst spherical recess.
 41. The axial piston machine as recited in claim40, wherein a first radius of the first spherical recess is equal to arunning surface radius of the spherical running surfaces.
 42. The axialpiston machine as recited in claim 39, wherein the bridge includes asecond spherical recess on an inner side having a larger radius than thefirst spherical recess, the second spherical recess being adapted to acontour of the at least one of the tilting ring and the tilting plate43. The axial piston machine as recited in claim 42, wherein the secondspherical recess enables the bridge to shift toward the at least one ofthe tilting ring and the tilting plate, respectively.
 44. The axialpiston machine as recited in claim 42, wherein due to the secondspherical recess, a bending line of the brace is so close to the atleast one of the tilting plate and the tilting ring, respectively, thata stiffness against bending during a suction movement is only slightlyreduced compared to a brace without a first spherical recess.
 45. Theaxial piston machine as recited in claim 30, wherein the brace definesan inner radial region facing the at least one of the tilting plate andthe tilting ring and an outer side, and wherein the outer side includesa sliding surface having at least one opening to the inner radial region46. The axial piston machine as recited in claim 45, wherein the atleast one opening supplies a lubricant to the sliding surface.
 47. Theaxial piston machine as recited in claim 45, wherein the at least oneopening includes a plurality of differently shaped openings.
 48. Theaxial piston machine as recited in claim 45, wherein the sliding surfaceincludes a pocket-shaped region formed in the sliding surface opposite adrive mechanism housing wall, the pocket shaped region providing arunning surface, and being supplied via at least one opening.